Photochemical stencil and method for manufacture



J 1951 D. E. HANSON EI'AL 2,969,014

PHOTOCHEMICAL STENCIL AND METHOD FOR MANUFACTURE Filed Feb. 19, 1958 INVENTORS Donald! if Jfmzsozz BY Mary K, drmsbee United States Patent PHOTOCHEMICAL STENCIL AND METHOD FOR MANUFACTURE Donald E. Hanson, Park Ridge, and Mary K. Ormsbee, River Forest, 11]., assignors to A. B. Dick Company, Niles, 111., a corporation of Illinois Filed Feb. 19, 1958, Ser. No. 716,099

'5 Claims. (Cl. 101-1283) This invention relates to a multiple copy process and it relates more particularly to a new and improved photochemical stencil and to the method for the preparation of a stencilized master therefrom.

For the most part, the stencil duplicating process for the preparation of multiple copies makes use of a stencil sheet formed of a stencil base tissue which is provided with a continuous coating of an ink impervious material which prevents the passage of ink but which is formu- "lated to permit displacement of the coating responsive without blocking the passage of ink from the plate cylinder to the copy sheets brought into surface contact therewith.

The described normal method for the preparation of the imaged stencil is not applicable to the preparation of 'a stencil either directly or indirectly from an original.

For this purpose, use has been made of a stencil sheet embodying a coating containing a light-sensitive material which operates upon exposure to render the coating insoluble so that the coating can be dissolved out from the unexposed areas to provide the stencil openings.

This process for the preparation of the imaged stencil from an original or negative by photochemical means embodies an excessive number of steps and requires the use of a large number of materials and it is for these reasons undesirable. Further, in the present photochemical process, the stencil sheet is sensitized almost immediately prior to use. Thus the preparation depends upon a treatment to be effected by the user at the diflerent stations of use thereby to limit the use of the stencil and thereby also to incorporate a human element which sometimes leads to wide variations in the performance and operation of the plate.

There is a need for a photochemical stencil which has shelf life sufiicient to permit manufacture from a common source of supply and which can be processed in a vsimple and etficient manner to produce an imaged master from which copies of good quality can be produced.

Thus it is an object of this invention to produce a new and improved photochemical stencil and it is a related object to provide a new and improved process for use in imaging same.

More specifically, it is an object of this invention to produce a stencil sheet which can be imaged for reproduction from an original; which can be prepared at a common source of supply in a simple and economical *manner; which can be fabricated of low cost and readily available materials; which avoids the necessity for sensi- -tization at the station of use, and which can therefore be presensitized long in advance of the use of the stencil at a common source for supply; which has good shelf life and stability; which can be imaged in a simple and efficient manner without the use of extensive equipment and labor and without an excessive number of operations, and which can be used as a conventional stencil on a stencil duplicating machine to produce a large number of copies of good quality.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing in which:

Fig. 1 is a perspective view partially in section of a stencil sheet embodying the features of this invention;

Fig. 2 is a perspective view similar to that of Fig. 1 showing a modification in the construction of a stencil sheet embodying the features of this invention;

Fig. 3 is a perspective view similar to that of Fig. 1 illustrating the construction of the stencil sheet following exposure, and

Fig. 4 is a perspective view similar to that of Fig. 1 showing the constructionof the stencilized stencil sheet.

The described objections have been achieved, in accordance with the practice of this invention, by the incorporation of some of the concepts of the diffusion transfer process employed for the production of single copies to the preparation of an imaged stencil from which a large number of copies can be produced.

The diffusion transfer process as applied to the manufacture of single copies is described in the Rott Patent No. 2,352,014. In the described single copy process a photographic image of an original produced in a silver halide layer is caused to produce a reverse image'on a copy sheet, provided the silver halide layer, after being exposed to light for the production of a latent image and then being impregnated with a developer to develop the image, is pressed or squeezed in the presence of a fogging agent and a solvent for the silver halide onto the copy sheet while the layer is still imbibed with the developing liquid. That part of the silver halide in the layer which is not reduced during development of the ex posed negative and which, in the ordinary photographic process, would be fixed. out in the fixing bath will transfer by ditfusion to the surface of the copy sheet to provide a reverse image thereon. In order to render this image freely visible, the light-sensitive layer containing the master image will normally be removed from the copy sheet.

In the Rott process, use can be made of the silver halide solvent contained in the usual photographic developers, such as sodium sulfite, sodium thiosulfate and the like. As fogging agents, use is made of a substance capable of promoting the reduction of silver halides without requiring the action of light, such for example as colloidal silver, colloidal forms of sulphur, silver sulfides, hypophosphites, stannous chloride, and organic compounds which are capable of splitting off sulphur in the form of bivalent ions, as represented by thiosinamine and thiocyanates. Such fogging agents are preferably embodied in the copy sheet during the manufacture thereof or they can otherwise be incorporated by a subsequent coating or impregnation.

The concepts of this invention are embodied in the manufacture of a stencil which is capable of development by a diffusion transfer technique to provide a one step exposure process for imaging the stencil directly from an original. The stencil is fabricated in accordance with the practice of this invention of a conventional base tissue 10, such as is formed of Kozu fibers and the like,

to app ied fo ce. he s en i shee employe n th p tice of :this invention is provided with a continuous coa ing 12 of a ha den d a n form lated to con a n a hu lcat or in a nt of t e yp which will react with the silver salts transferred by diffusion from the expos d. ne at v t orm a ilver image A degradation o the gela i n he i age area, which en elimination of the gelation coating in the imaged area, is

hrotls a o t by trea ent with an acid etch nd the .l e

White ammonium or alkali metal thiosulfates, dithiooaam e, th os ha i.he, argyrol and the i g agents, preferably employed as fogging agents in the copending application of Regan, Jr. et al., Ser. No. 498,192, for use in the, manufacture of an imaged lithographic plate,

might be used, it is preferred to make use of a nucleating or reactive agent which operates to form a more dis P FSGd image in the coating thereby to achieve better and more complete degradation of the gelatin to enhance removal from the imaged areas of the coating. For this purpose, it is preferred to make use of materials of the type previously described as being employed in the single copy process of Rott and best results are secured in the combination which makes use of a sulfide in the, form of ammonium or metal sulfide and preferably an alkali metal sulfide such as sodium or potassium sulfide and a soluble silver salt such as silver nitrate. The combination of materials can be used in the coating in combination with other nucleating agents as listed above, such as ammonium thiosulfate and the like.

It is sufficientwhen the nucleating materials are present in the gelatin coating in .an amount greater than 0.05 percent by weight of the coating. It is preferred to make use of the nucleating agent in a concentration in the coating ranging from 0.1-0.5 percent by Weight of the coating. The upper limit of concentration is not critical but little additional benefit is derived from the portions of the nucleating agent which are present in an amount greater than 2 percent by weight of the coating and use in amounts greater than described leads to difficulties in formulation and in the characteristics of the coating that is formed on the stencil base tissue.

When the complex silver salts transfer by diffusion from the unexposed portions of the negative to the gelatin coating, the salts are reacted with the nuclcating agents in the coating to produce a dispersed silver image.

The, subsequent etching reaction leads to the degradation of the gelatin in the imaged areas 14 of the coating which reduces the gelatin to a condition which enables it to be removed by the treating or etching solution which has no effect on the unreacted, hardened portions of the gelatin emulsion or coating in the non-imaged areas. This leaves the hardened gelatin in the non-imaged areas while the gelatin coating in the imaged areas is removed to provide stencil openings 16 through which the ink may pass.

While best results are secured by the use of gelatin in an emulsified form in the manufacture of the coating 12 on the stencil base sheet 10, gelatin in other hardenable forms can be used. Though not exactly equivalent,

other proteinaceous colloids, such as the alginates, caseins,

albumens and the like, may be used as the polymeric material forming the coating and containing the nucleating substances leading to the degradation of the colloid n t s e wnta n s ma ed ar as e o n up re t on with. he e chin i reatin s n- T e tol wins i i us rate t e pr c i e f h sh icn in. he fabricat on o ne ad mp ov ar sensitized stencil sheets and in the use thereof to image the stencil from an original:

EXAMPLE 1 Stencil sheet manufacture The materials are formulated into a hot melt at a temperature of about F. and applied to form a coating onto a high wet strength stencil base tissue having about 5 pounds basis weight. The coating is applied in amounts to provide a coating weight of 3 grams per square meter and then the coated base tissue is sheeted into stencil sheets. The coating may be achieved by conventional roller coating processes or other conventional coating processes represented by the dip squeeze process and the like. Coating weights other than 3 grams per square meter may be employed including weights as low as 2 grams per square meter to as high as 10 grams per square meter but it is preferred to keep the coating weight on the low side so as to facilitate the removal of the coating in the imaged areas of the stencil sheet during the subsequent etch treatment. While the drawing will illustrate the stencil coating as being concentrated on the surface of the stencil base sheet separate and apart from the base tissue, it should be understood that the stencil base tissue will for the most part be penetrated an s bs ant ly c mp e y impr na d by the coat n compo itio EXAMPLE 2 P para i of the imaged ste c ferred, in this process, to make use of a photographic negative which is transparent or translucent in order to provide maximum latitude of the original. The photographic negative does not have to be flexible and the thickness and dimension of the negative are of relative unimportance in this process. By way of example, a suitable negative is marketed by AGFA under the trade name Copyrapid.

The exposed photographic negative is developed in a solution containing the normal developing components employed in the photographic art plus a material which is capable of functioning as a solvent for the silver halide or the silver halide complex that is formed. For this purpose, use can be made of a typical mono-bath developer including a developer and a fixer such as are ordinarily employed in the photographic practice, as represented by a solution formulated of the following:

.0 gr m hydroq n n 310 rams so iu hy o 40 grams sodium sulfite (silver halide solvent). 1 0 grams sodium thiosulfate (silver halide solvent); 1.5 grams bcnzotriazole.

Water sufficient to make up 1 liter.

tissue and with one or the other or both of the surfaces wet with the developing solution. In the preferred practice of this invention, the exposed negative and the stencil base tissue will be run together into a bath of the developing solution and then will be brought into surface contact with each other between squeeze rolls as the sheets issue from the developing solution. As the surfaces are brought into contact with each other during development, the soluble silver complex formed of the silver halide present in the unexposed portions of the negative coating transfers by diffusion to the corresponding areas of the stencil coating 12. Transfer may be instantaneous upon contact but it is preferred to provide means for maintaining contact for a greater length of time ranging from a few seconds up to as much as 2 minutes. For a detailed description and illustration of the exposure steps and the developing steps for difiusion transfer, reference may be made to the copending application of Regan, Jr. et al., Ser. No. 498,192, filed March 31, 1955.

The silver nitrate and sodium sulfide together or in combination with the ammonium thiosulfate in the stencil coating 12 promote the reduction of the silver halide complex that is transferred to the stencil coating to produce a silver image. A degradation of the gelatin in the imaged areas to reduce the gelatin to a form capable of being removed from the stencil base sheet is brought about by treatment with an acid etch solution as represented by the following composition published by Eastman Kodak Company under the designation EB-2.

Preparation of etch solution 750 cc. water, 120 grams copper sulfate, 150 grams citric acid and 7.5 grams potassium bromide are dissolved in water in amounts to make up 1 liter.

In a separate container, a solution is formed containing about 3 percent hydrogen peroxide.

The two compositions are mixed to form a composite etch solution through which the processed stencil sheet is passed. The etch solution operates to degrade (probably by reaction with the silver and gelatin in the imaged areas) and remove the gelatin in the imaged areas to provide stencil openings 16 while it has practically no effect upon the hardened gelatin in the non-imaged areas so that the latter will remain as a coating on the stencil base tissue to prevent the passage of ink. The processed stencil base tissue is treated by passage through the etch solution subsequent to its separation from the exposed negative.

Other well known etch compositions can be employed containing similar copper salts, bromides and acids efiective to remove the gelatin in the degraded areas.

The formed stencil can be mounted on a conventional ink cylinder of a stencil duplicating machine to produce multiple copies. It will be apparent that the concept described can also be employed as a photochemical means for the preparation of stencils used in the silk screen processes for printing and the like.

The concepts herein described are capable of being adapted to a one sheet process wherein the negative coating is embodied as a component of the stencil sheet. In such modification, the colloid coating containing the silver halide of the conventional negative is fabricated as an overcoating on the coating 12 applied to the stencil base tissue 10.

The following will represent this further modification in the concept of this invention in the manufacture of a stencil base sheet illustrated in Fig. 2 of the drawing:

EXAMPLE 3 To the point where the stencil base sheet 10 is formed with the coating 12 of a hardened ink impervious colloid, the process corresponds to that of Example 1. The negative coating 20 is applied as a separate coating onto the 6 surfaceof the coating 12. The negative coating is of a conventional formulation represented by the following:

In formulation of the coating composition, mixtures A and B are combined and then mixture C is added and the composite is digested for 16 minutes at about F. Prior to application of the coating composition onto the previously applied coating 12, the final materials are added including 0.2 gram citric acid, 12.0 ml. ethyl alcohol and 2.8 ml. of water.

The final composition is mixed and applied by conventional coating means at a temperature of about 120 F. and in a coating weight of about 10-20 grams per square meter.

Exposure with the original operates in the same way as a conventional photographic negative to produce a latent image in the silver halide coating 20 without effect on the underlying colloid coating containing the nucleating agents. Transfer of the soluble complex silver salts from the non-exposed portions of the negative coating 20 to the underlying stencil coating 12 during development by the fixing and developing bath containing a solvent for the silver halide occurs by diffusion from the one coating to the other during the development by the fixing and developing bath containing a solvent for the silver halide. The negative coating and the imaged portions of the colloid in the stencil coating 12 are all removed by the etch solution to produce the imaged stencil.

It will be understood that the exposure technique is similar to that employed in the conventional photographic art.

The described stencilization of a stencil by photographic technique from an original embodies the simplicity char acteristic of the diffusion transfer process to provide a means for stencilization capable of use with a wide range of originals. The concepts of this invention permit the preparation of a stencil master from many types of originals by reflex, print-through contact or projection printing methods.

The prepared stencil is prehardened and insensitive to light so that it can be prepared in quantity for storage and shipment to distant stations of use with readily available presensitized negative papers. The described concept further provides a simple, rapid and economical means for producing an imaged stencil master by a photographic technique.

It will be understood that changes may be made in the various formulations and materials and in their method of application and use without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. A photochemical stencil comprising a stencil base tissue and an ink impervious coating on the stencil base tissue formed of a hardened proteinaceous colloid containing a nucleating agent for the release of silver upon reaction with a silver halide complex.

2. A photochemical stencil as claimed in claim 1 in which the colloid in the layer is selected from the group consisting of gelatin, alginate, albumen and casein.

3. The method of imaging the photochemical blank defined by claim 1 comprising the steps of transferring a silver halide complex to form image areas on the colloid coating wherein a reaction takes place to release a silver image with subsequent degradation of the colloid, and

"7 mnevingthe degraded colloid in. the. im g d areas to provide ten il openings through which ink may pass.

4. The method of imaging the photochemical blank .defined by claim 1 comprising the steps of exposing an original to a-silver halide coating of a negative to provide railatent image of unreacted silver halide'in the unexposed portions of the negative, developingthe negative while in surface contact with the stencil sheet with a developing solution containing a solvent "for the silver halide remaining in the unexposed portions of the negative to cause transfer by diffusion from the negative to the stencil coating, separating'the negative from'the stencil sheet, and treating the processed stencil sheet with an etch solution to degrade and dissolve out the colloid in the silverimage areas resulting-from the reaction of the silver halide with 15 2,665,986

References Cited in the fileof this parent UNITED STATES PATENTS 1,494,667 Coe l May 20, 1924 I 1,588,574 Gestetner June 15, 1926 2,352,014 Rott June 20, 1944 Rott Jan. 12, 1954 el -mil... 

